At 15:50 (GMT+2) I flipped the switch for all the game clients. The RSPs are gradually enabling the map pack on game servers.
It includes the following two levels:
Atacama Desert, Rush (code name "levels/mp_005gr")
Port Valdez, Conquest (code name "levels/mp_012cq")
If you are a player
There are already some servers up & running the new maps. Go look for them in the server browser!
The search filters in your game client will be updated if you restart BFBC2.
If you are a server administrator
The maps are available to your server once your RSP has performed a configuration change [essentially: added a commandline option].
After that the server needs to be rebooted. Then server will recognize the new maps in maplist.txt.
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http://twitter.com/OfficialBFBC2 From the new guy at EA UK forums
http://forums.electronicarts.co.uk/battlefield-bad-company-2-pc/1215551-map-pack-4-out-now.html